CURRICULUM VITAE Dr. LEONIDAS D. DRITSAS 12 September...

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CURRICULUM VITAE

Dr. LEONIDAS D. DRITSAS 12 September 2012

1. GENERAL INFORMATION ............................................................................. 3 2. STUDIES .............................................................................................................. 3 3. FOREIGN LANGUAGES - COMPUTING ..................................................... 4 4. PROFESSIONAL EXPERIENCE .................................................................... 4 • Hellenic Air Force (Ministry of National Defense) and Hellenic Air Force Academy Jan. 2007 – present ........................................................... 4 • OTE (Hellenic Telecommunications Organisation) Jul/1997-Jan/2007 4 • ABB (Asea Brown Boveri ) Mar/1994 – July/1997........................ 5 • ZENON S.A Jan/1990 - Mar/1994 .................................... 5 • Greek Armed Forces (Military Service) Nov/1988-Jun/1990 ............. 5 • Gen. Sec. of Research and Technology Jan/1987-Oct/1988 . 5

5. TEACHING EXPERIENCE ............................................................................ 6 6. RESEARCH ACTIVITY ..................................................................................... 7

A. Research Activities after the PhD studies ............................................ 7 B. European Research Projects (during/before the PhD studies) ........... 7

7. PUBLICATIONS ................................................................................................ 8 Seven (7) published Journal papers and one(1) recently accepted, ........... 8 Two(2) Book Chapters ................................................................................ 8 Twenty seven (27) Conference Papers ....................................................... 8

8. INTERNATIONAL PRESENCE (Citations, Chairmanships, Reviewing, Invitations) ...................................................................................... 8

C. Citations ................................................................................................ 8 D. Alternative Web Resources (Google Scholar, IEEE Explorer) ............. 9 E. Three “Chairmanships” in recent Intl. Conferences ............................... 9 F. Review Work for eight (8) Intl. Journals ................................................ 9 G. Review Work for thirteen (13) recent Intl. Conferences .................... 10 H. Workshops and Tutorial Conference Speaker ...................................... 10

9. GENERAL INFORMATION ........................................................................... 10 • Professional Qualifications/Memberships ............................................. 10 • Extra-Curricular Activities / Social Interests ......................................... 11 • Other Information................................................................................ 11



APPENDIX “A” - Publication List with Abstracts ............................................ 12 Α.1 Journal Publications (7 published 1 accepted) ................................ 12 Α.2 Two(2) Book Chapters ..................................................................... 15 Α.3 Twenty Seven (27) Reviewed Conference Papers (Proceedings) ..... 16



Dr. LEONIDAS D. DRITSAS

1. GENERAL INFORMATION Name : Leonidas Dritsas Date of Birth : 12/Nov/1962 Address : Kleitou 8, Zografos 15771 Telephone(s) : + 30-210-7779392 (Home) and +30-6983-519-273 (Mob) Marital Status : Married, one child Mail : [email protected] & [email protected] Skype : leonidasdr 2. STUDIES

• Mar. 2004 - Mar. 2009 : Ph.D in the Control Engineering section of the E.C.E Dept. University of Patras, GREECE. Defended 05-Feb-2009, Awarded 06-May-2009.

Dissertation Title (PhD Thesis): “Robust Control of Networked Systems” (in Greek) Please visit the Department’s site http://www.ece.upatras.gr/en_index.php , the web page of our research team ( http://anemos.ece.upatras.gr/ ), my supervisor’s page (http://anemos.ece.upatras.gr/index.php/people/tzes ) and my page as Researcher http://anemos.ece.upatras.gr/index.php/people/completed-phd-thesis/leonidas-dritsas )

• Sep. 1985 – Dec. 1986: M.Sc in Electrical and Computer Engineering E.C.E Dept., Drexel University, Philadelphia, USA

Dissertation Title (Master Thesis): "Robust Nonlinear Robot Control". Principal subjects covered: Robotics, Control Engineering, Automation and Mechatronics. During my graduate studies I had a Teaching Assistantship (later turned into a Research Assistantship) from the E.C.E Dept. of Drexel University. I was responsible for the "Electric Machinery" Laboratory exercises of the undergraduate students. (pls. visit http://www.ece.drexel.edu/ and my supervisor’s page at http://www.ece.drexel.edu/faculty/guez/ Prof. Allon Guez)

• Oct. 1980 – Aug. 1985: Diploma in Electrical Engineering, Graduation grade: 8.7/10(Excellence), E.C.E Dept. University of Patras, Greece.

Specialization in Control Systems, Robotics and Electrical Machinery. During my undergraduate studies I was awarded three scholarships for excellent performance. Final Year Thesis: “Self Tuning Controllers”

• 1974 - 1980: Varvakios Model School Graduation grade : 19 (Excellent)



3. FOREIGN LANGUAGES - COMPUTING

• English : Fluent (Certificate of Proficiency in English, Cambridge University) • French : Moderate (only technical reading) • Good knowledge of PCs (MS-Office, Windows), UNIX, Networking, RDBMS, LaTex,

Scientific packages (MATLAB). Programming experience in FORTRAN & C. 4. PROFESSIONAL EXPERIENCE

• Hellenic Air Force (Ministry of National Defense) and Hellenic Air Force Academy Jan. 2007 – present

Positions: Chartered Electrical Engineer at the Hellenic Air Force (Ministry of National Defense) and at the same time an Adjunct Lecturer at the Hellenic Air Force Academy (Academic Years 2009-2010 & 2010-2011). Main activities and responsibilities: My first assignments (Jan.2007 - Aug 2010) were with the Air Force Training Command (“HAFTC“ http://www.haf.gr/en/structure/units/dae/ ) , and the Hellenic Air Force Academy (“HAFA” http://www.haf.gr/en/career/academies/si/ ). Main responsibilities were the technical-economic evaluation of bids, the operation and maintenance of the electro-mechanical installations of the Command and of “HAFA’s” new campus. On Aug. 2010 moved to Hellenic Air Force Headquarters acting as Senior Project Manager for various Electrical Engineering projects.

Starting from Oct. 2009 also employed as Adjunct Lecturer at the Hellenic Air Force Academy, Division of Automatic Control, teaching a course on Applied Control Systems and running the Electric Machines Laboratory.

• OTE (Hellenic Telecommunications Organisation) Jul/1997-Jan/2007 Positions: Senior ICT Engineer at OTE S.A. (Hellenic Telecommunications Organization www.ote.gr ), 99 Kifisias Ave., Amarousion , GR-115 81 Athens Greece Type of business or sector: Hellenic Telecommunications Organization (OTE S.A.) is the incumbent telecommunications provider in Greece, and together with its subsidiaries forms one of the leading telecom groups in Southeastern Europe. Main activities and responsibilities: My first assignments concerned Network Management Systems (NMS) and the deployment of Broadband Networks (ATM, IP/MPLS, ADSL, Metropolitan Ethernet). For two years (2000-2002) I served as IT Administrator for the “Digital Broadcast Satellite” Platform developed by OTE for Pay TV distribution and “Fast” Internet services. For another two years (2002-2004) I was Head of the IT Dept. at OTE Estate S.A. (http://www.ote-estate.gr/Company/AboutUs/tabid/82/language/en-US/Default.aspx), an OTE subsidiary, deploying the IT infrastructure and the ORACLE e-Business suite application.

The last two years of his employment at OTE S.A, I was in charge of the Service Management Department , involved with the deployment of procedures concerning Service Fulfillment, Service Assurance and SLA Management for the large corporate customers of OTE S.A.



• ABB (Asea Brown Boveri ) Mar/1994 – July/1997

Position: Technical Sales and Application Engineer, Dept. of Drives and Automation. Main activities and responsibilities: I was responsible for the activity of “Variable Speed Drives, Large Motors” and also acted as member of the Industrial Automation Task Force of the company (www.abb.com) . I was involved in all phases of the corresponding projects (quotation, order handling, application engineering, installation, start-up and maintenance). I was trained twice in ABB Industry Oy (Helsinki, Finland) for AC motors and Drives and in ABB Industrietechnik (Mannheim, Germany) for DC Drives. Contributed in the start-up of a new activity within the Greek Branch of ABB, that of “Instrumentation and Process Control”.

• ZENON S.A Jan/1990 - Mar/1994

Position: Project Manager R & D Department

Type of business or sector: Since its foundation (1988), the main activities of ZENON S.A. (www.zenon.gr) were in the field of industrial automations, Robotics, in high technology co-funded research programs and also in the field of Informatics mainly for the public sector. Main activities and responsibilities: I was involved in various EU Research Projects (ESPRIT, BRITE, IST) in the areas of Robotics and Automation.

I managed an ESPRIT Research Project as Leader of the Consortium (ESPRIT 2640 “Integrated Process Control and Inspection in Robot Finishing”). This project finished successfully Febr. 1992 and developed a Robotic Grinding/Finishing work cell enhanced with “Computer Vision” Quality Control subsystem. An Industrial prototype was presented in Hannover Fair 1994 and was later modified for the finishing of turbine blades. At the same time involved in Automation and Robotic Work cell installations (welding and palletizing) in the Greek and Cypriot Industry.

• Greek Armed Forces (Military Service) Nov/1988-Jun/1990

Position : Computer Specialist at the Ministry of Defense Served the Greek Armed Forces. After a five-month military training, I was employed as a top-secret Computer Specialist at the Defense Planning Dept. of the Ministry of Defense. (Financial applications using RDBMS tools in a UNIX environment)

• Gen. Sec. of Research and Technology Jan/1987-Oct/1988

Position : Project Evaluator & IT Engineer Member of the IT Dept. of the Ministry of Industry – General Secretariat of

Research & Technology (www.gsrt.gr) . My duties included the installation of new hardware and computer networks, the development of apllications using RDBMS tools in a UNIX envronment, and the dissemination of these technologies in the civil sector through seminars and presentations.

At the same time, and in parallel with my work at the "Informatics" Dept., I served as an evaluator of the research proposals submitted for financing to the Ministry of Research and Technology by the Greek Industry and Academia.

Starting on January of 1987 I was also member (Researcher) of the “ Intelligent controls and Robotics“ research team at the (“NTUA”) National Technical University of Athens (Prof. S.Tzafestas), working mainly in European Research Projects (ESPRIT 278 –“Tactile



sensing for Integrated Sensor Based Robot Systems”) and teaching undergraduate courses in Controls and Robotics. 5. TEACHING EXPERIENCE My Teaching Portfolio includes two years in a University (H.A.F.A) and six years in a Technology Institute. All my teaching activity concerns Control Engineering Courses and Laboratories. In this context I have written Lecture Notes and supervised Final Year Thesis. • Adjunct Lecturer at the Hellenic Air Force Academy (H.A.F.A) for the

Academic Years 2009-10 & 2010-11. Starting from Oct. 2009, and in parallel with my Duties in Hellenic Air Force, was employed as Adjunct Lecturer at the Hellenic Air Force Academy, Division of Automatic Control, teaching a course on Applied Control Systems and running the “Control Systems & Electric Machines Laboratory”. The appointment is expected to continue for a third Academic Year (2011-2012) Three(3) Final Year Thesis Supervised at Hellenic Air Force Academy

- (2010-2011): “Stability Analysis and Synthesis of Tracking Controllers for a Guided Missile” (in Greek).

- (2011-2012): “Design of H∞ / Mixed Sensitivity Multivariable Controller for a guided missile” and “Design of Multivariable (Regulation and Tracking) Controllers based on the H∞ / Mixed Sensitivity approach”.

Lecture Notes (in English) concerning Robust Control , LMIs and Tracking Controllers, freely available at http://users.otenet.gr/~ldri • Instructor at the Technology Institute of Chalkida (T.I.C) - Dept. of

Automation for six Academic Years (2004 to 2010) Instructor at the Dept. of Automation (http://www.aut.teihal.gr/ ) of Technology Institute of Chalkida (TIC http://www.teihal.gr/ ). Courses taught were: “Optimal Control and Kalman Filtering” (7th Semester) , “Introduction to Control Systems” (3rd Semester) Lecture Notes (in Greek) available at http://users.otenet.gr/~ldri Final Year Thesis Supervised at T.I.C (in Greek)

- “Synthesis of Linear Tracking Controllers” (2009) - “Applying Optimal Control to Financial Problems” (2008)

• Instructor and Final Year Thesis Supervisor at N.T.U.A (1987-1988)

Supervised one Thesis on “Robust Robot Control” (John Kannelakopoulos NTUA 1987)

• DREXEL University (USA) Teaching Assistantship and Recommendation Letter

As a graduate student I was awarded «Teaching Assistantship» from the ECE Dept. of Drexel University (1986-1987) and served as Instructor at the Electric Machine Laboratory (2 semesters). This was later changed into “Research Assistantship”. The available



documentation includes a recommendation Letter from my MSc Thesis supervisor Prof. Allon Guez.

6. RESEARCH ACTIVITY

A. Research Activities after the PhD studies I am continuing my research activities with the E.C.E Dept. U. of Patras mainly with Prof. Anthony Tzes (pls. see http://www.ee.upatras.gr/en/pr_meli_dep_pl.php?id=5 and http://anemos.ece.upatras.gr/index.php/people/tzes ) and Prof. George Bitsoris (http://www.ee.upatras.gr/en/pr_meli_dep_pl.php?id=16 ).

See also my webpage as “Post Doc Researcher” at the University of Patras, ECE Dept.

http://anemos.ece.upatras.gr/index.php/people/completed-phd-thesis/leonidas-dritsas

There is also a research collaboration with Prof. George Halikias (City University, UK) and Prof. Athanasios Pantelous (U. of Liverpool, UK) and Dr. V. Tsoulkas concerning a control theoretic research of non overshooting stabilization (“strong stability”).

A recent collaboration concerning flight control applications started at the Control System Lab. at NTUA (http://www.controlsystemslab.gr/ Prof. K. Kyriakopoulos http://site.csl.mech.ntua.gr/main/ ).

B. European Research Projects (during/before the PhD studies)

B1. “HYCON” Network of Excellence (2004 – 2006, 18 months) Eighteen (18) months participation in the Network of excellence “HYCON” (=Hybrid Control Systems) from September/2004 – February/2006 (see http://www.ist-hycon.org).

B2. “RUNES” IST Project (2004 – 2006, 15 months) Fifteen(15) months participation (Dec.04 – Feb.06) at the IST Project RUNES (IST-004536) «Reconfigurable Ubiquitous Networked Embedded Systems” (see http://cordis.europa.eu/fetch?ACTION=D&CALLER=PROJ_IST&RCN=71577 also ftp://ftp.cordis.europa.eu/pub/fp7/ict/docs/necs/20080228-04-runes-results_en.pdf and old site at http://www.ist-runes.org )

B3. “COLOMBUS” IST Project (2004, 3 months) Three(3) months participation (Apr.04 – June.04) at the IST Project “COLOMBUS IST-2001-38314– Design of embedded controllers for safety critical systems” (see http://www.columbus.gr/ )

B4. The “PANACEIA-ITV” IST Project (2002-2003, 24 months) Twenty four(24) months participation at the IST Project “PANACEIA-ITV”- IST Project (IST-2001-33369 The PANACEIA Health System) as member of OTE’s R&D Dept.



(“Digital Broadcast Satellite” Platform) (funded by the CEC. Scientific Coordinator, 8/2001 – 5/2004, Cost 4,2 MEUROs http://cordis.europa.eu/fetch?ACTION=D&CALLER=PROJ_IST&RCN=61019)

B5. The “ESPRIT Project 2640” (1990 - 1992, 24 months) Project Coordinator for the Research Project “ESPRIT2640 - Integrated Process Control and Inspection in Robot Finishing” as ZENON S.A employee (see http://research.cs.ncl.ac.uk/cabernet/www.laas.research.ec.org/esp-syn/text/2640.html and http://cordis.europa.eu/search/index.cfm?fuseaction=proj.document&PJ_LANG=EN&PJ_RCN=364231 )

B6. The “ESPRIT Project 278” (1987-1988) Member of the research team at Nat. technical University of Athens (Prof. S. Tzafestas) working for the ESPRIT 278 Research Project – (“Tactile sensing for Integrated Sensor Based Robot Systems”). 7. PUBLICATIONS

Seven (7) published Journal papers and one(1) recently accepted,

Two(2) Book Chapters

Twenty seven (27) Conference Papers

Please see Appendix A (“DRITSAS Publications”)

8. INTERNATIONAL PRESENCE (Citations, Chairmanships, Reviewing, Invitations)

C. Citations Using the (freely available) “Publish or Perish” application and setting “L Dritsas” in the field “Author’s Name” while chosing “Engineering,Computer Science,Mathematics” ) the following results are given (14-Oct-2011): see http://www.harzing.com/pop.htm?source=pop_3.1.4004 also http://www.harzing.com/pophelp/metrics.htm and http://www.harzing.com/pop_hindex.htm )

• Total number of papers Papers:35, • Total number of citations Citations:120, Years:26, • Cites/year:4.62, • Cites/paper:3.43, • Average number of citations per author Cites/author:49.16, • Average number of papers per author Papers/author:13.53, • Average number of papers per author Authors/paper:2.88, • Hirsch's h-index h-index: 7



D. Alternative Web Resources (Google Scholar, IEEE Explorer) Google Scholar see http://scholar.google.com/scholar?oi=bibs&hl=en&q=Leonidas+Dritsas

and http://scholar.google.com/citations?hl=en&user=jXz1fzEAAAAJ&view_op=list_works&gmla=AJsN-F6D7HwKxeIsU5HAhSNOcmFqkSvqPNQHncuIyYAQVZC1erzoQlCi4v7kO2W4BB5l8V-8XOEF9MWQLlh2TuIygDkLpPi0f_F4tbwTsu3tyLHAraZMdGgbY4mQkPm14-vDknz5Flmd IEEE Explorer http://ieeexplore.ieee.org/search/freesearchresult.jsp?newsearch=true&queryText=Dritsas%2C+L.&x=0&y=0

E. Three “Chairmanships” in recent Intl. Conferences

[1] Session chairman for the "Networked Control Systems II (WeB09)" session at the 2007 American Control Conference, New York City, USA , July 11-13, 2007 (https://css.paperplaza.net/conferences/conferences/2007ACC/program/2007ACC_ContentListWeb_1.html#web09) [2] Session chairman for the "Uncertain Systems III" WeD06 Regular Session at the European Control Conference 2007 , Kos, Greece 2-5 July 2007 (https://euca.papercept.net/conferences/conferences/ECC07/program/ECC07_ProgramAtAGlanceWeb.html) [3] Session chairman for the Networked Control Systems II (Regular Session) Thursday, June 25, 2009, 12:00-13:40, The 17th Mediterranean Conference on Control & Automation, MED 2009, Thessaloniki, Greece Jun 24 -26, 2009. http://www.med09.org/

F. Review Work for eight (8) Intl. Journals

1. IEEE Transactions on Automatic Control (1 paper - November 2005) 2. IEEE Transactions on Control Systems Technology (1 paper ,

September/October 2010) 3. International Journal of Robust and Nonlinear Control (1 paper,

August/September 2010) 4. IMA Journal of Mathematical Control and Information

http://imamci.oxfordjournals.org/ (1 paper, October/December 2010) 5. Simulation Modelling Practice and Theory - http://ees.elsevier.com/simpat/ (1

paper, January - March 2011) 6. International Journal of Control (1 paper – Dec. 2011) 7. Automatica (1 paper – Nov. 31 Dec. 2011)



8. IEEE Transactions on Control Systems Technology (1 paper -January – March 2012)

G. Review Work for thirteen (13) recent Intl. Conferences

1. CDC 2006 (IEEE Conference on Decision & Control

http://www.ieeecss.org/CAB/conferences/cdc2006/index.php ) 2. ECC 2007 (European Control Conference http://ecc07.ntua.gr/ ) 3. IFAC 2008 (2 papers) (International Federation of Automatic Control

http://www.ifac2008.org/ ) 4. ACC 2009 (3 papers) (American Control Conference

http://www.a2c2.org/conferences/acc2009/ ) 5. ECC 2009 (3 papers http://www.conferences.hu/ecc09/ ) 6. MED 2009 (3 papers http://www.med09.org/ ) 7. ACC 2010 (1 paper) (American Control Conference

http://www.a2c2.org/conferences/acc2010/ ) 8. ISMS 2010 (4 papers) (International conference on. Intelligent Systems,

Modelling and Simulation http://www.isms2010.org.uk/ ) 9. UKSIM 2010 (2 papers) - 12th International Conference on Computer Modelling

and Simulation (http://www.uksim2010.org.uk/ ) 10. ICECS 2010 (2 papers) - The 17th IEEE International Conference on Electronics,

Circuits, and Systems (http://www.icecs2010.org/ ) 11. UKSIM 2011 (2 papers) - The 13th International Conference on Computer

Modelling and Simulation (http://www.uksim2011.info/ ) 12. CDC/ECC 2011 (1 paper) - 50th IEEE Conference on Decision and Control and

European Control Conference (http://control.disp.uniroma2.it/cdcecc2011/ ) 13. ICIT 2012 (3 papers) - the 2012 IEEE International Conference on Industrial

Technology (http://icit2012.isi.gr/ )

H. Workshops and Tutorial Conference Speaker

1. Invitation as Speaker at a Workshop held at U. of Liverpool ( Math. Dept.,

RESEARCH CENTRE IN MATHEMATICS AND MODELLING Prof. Athanasios Pantelous and Prof. Alexander Movchan) “Challenges in Network-Centric Control and Communication Systems, Liverpool 29June10” . My presentation was about ”Robust Control over Networks with varying delays”

2. Coauthor (with Dr. Tsoulkas) of the Tutorial speech at the CICSYN2010 (2nd

International Conference on Computational Intelligence, Communication Systems and Networks - Liverpool, UK, July 29th, 2010 (see http://cicsyn2010.info/ and the PPT file at Keynote and Tutorial Speakers)

9. GENERAL INFORMATION

• Professional Qualifications/Memberships Member of the Hellenic Chamber of Engineers (Number 50131) Member of the Hellenic Association of Mechanical-Electrical Engineers



(Voted) Member of the Coordinating Board of the Greek Branch of FITCE (www.fitce.org) the “federation” of European Telecom Engineers. Participates in the organization of FITCE Congress 2002.

• Extra-Curricular Activities / Social Interests My spare time activities include listening to Μusic, Singing & Guitar playing Psychology/Philosophy readings, Tai Chi I also enjoy traveling, watching sci-fi films.

• Other Information I own a car and I have a clean driving license. ADDITIONAL INFORMATION AND REFERENCES ARE AVAILABLE UPON REQUEST



APPENDIX “A” - Publication List with Abstracts

Α.1 Journal Publications (7 published 1 accepted)

[J1] Spyros Tzafestas and Leonidas Dritsas “Combined computed torque and model reference adaptive control of robot systems” Journal of the Franklin Institute Volume 327, Issue 2 , 1990, pages 273-294 doi:10.1016/0016-0032(90)90022-B

Abstract: A new robust technique for robot control is presented which is based on a combination of the feedback computed torque (FCT) method with the model reference adaptive control (MRAC) algorithm. It is shown that perfect tracking is feasible despite the errors induced by a practical FCT controller based on an "imprecise" or "simplified" available robot model. The MRAC part of the controller is simpler than the ones customarily used for robot control, and only a minimum amount of information is required. The results are illustrated by a double link manipulator computational example.

***

[J2] L. Dritsas and A. Tzes, “Robust Stability Bounds for Networked Controlled Systems with Unknown, Bounded and Varying Delays” (περιοδικό IET Control Theory & Applications, Volume 3 Issue 3 (March 2009), pages 270 – 280 ( doi:10.1049/iet-cta:20070384 and http://dx.doi.org/10.1049/iet-cta:20070384 )

Abstract: A robust control oriented modelling approach for Networked Controlled Systems (NCS) with uncertain, varying, bounded transmission delays and asynchronous discrete–time control laws is presented. The derived model is used for the derivation of sufficient conditions for the robust stability of NCS and the computation of the maximum allowable delay (constrained within one sampling period) that the closed–loop system can tolerate given a preselected set of stabilizing gains for the nominally delayed system. The derived stability conditions can be used for both open loop stable and unstable systems and are numerically simple to use since they rely on singular value calculations and the solution of a standard discrete Lyapunov equation. The impact of certain designer choices (such as sampling period, nominal delay, and tuning parameters appearing in the stability conditions) on the delay range is also investigated. Simulation studies are used to investigate the efficiency of the derived robust stability bound.

*** [J3] L. Dritsas and Α. Tzes "Robust Stability Αnαlysis οf Networked Systems with Varying Delays" - “International Jοurnal οf Contrοl” Vol. 82, No. 12, December 2009, pages 2347–2355, first appeared Aug. 2009, DOI: 10.1080/00207170903061705 )

Abstract: This paper is concerned with Networked Controlled Systems (NCS) with uncertain, varying, bounded transmission delays and asynchronous discrete–time static control laws. It is first shown that the delay variation gives rise to a discrete–time uncertain NCS model; robust stability analysis is carried out via a linear matrix inequality approach which, when combined with a directed parameter search, yields an estimate of robust stability bounds against any variations of the maximum allowable delay (constrained within one sampling period) that the closed–loop system can tolerate. The derived bounds are compared with other techniques relying on the singular values of the perturbed NCS–model.



*** [J4] L. Dritsas and Α. Tzes “Computation of Robust Stability Bounds for Networked Systems with Varying Delays” Intl. Journal. Systems, Control and Communications, Inderscience Enterprises ( Accepted 08-January-2011 as Paper ID Number: IJSCC 10-P0301 - online since March 21, 2012 – DOI: 10.1504/IJSCC.2012.045929 Volume 4, Number 1–2/2012 ) (see http://inderscience.metapress.com/content/x815245w20501062/ ) Abstract: This paper is concerned with the computation of robust stability bounds for Networked Controlled Systems with uncertain, varying, bounded transmission delays. Given the feedback controller, the maximum allowable transmission delay is computed based on a Linear Matrix Inequality (LMI) constrained nonlinear optimization problem. Since certain variations of the posed problem, demand a nominally stable closed-loop system, a controller synthesis procedure is also presented. The computation of the stabilizing controller is based on a delay-dependent LMI feasibility problem. The derived robust stability bounds are compared in simulation studies.

*** [J5] G. Halikias, L. Dritsas, A. Pantelous and V. Tsoulkas “Strong stability of discrete-time systems” , Linear Algebra and its Applications http://www.elsevier.com/wps/find/journaldescription.cws_home/522483/description#description Volume 436, Issue 7, Pages 1890–1908, http://dx.doi.org/10.1016/j.laa.2011.09.024

Abstract: The paper introduces a new notion of stability for internal autonomous system descriptions in discrete-time, referred to as "strong stability", which extends a parallel notion introduced in the continuous-time case. This is a stronger notion of stability compared to alternative definitions (asymptotic, Lyapunov), which prohibits systems described by natural coordinates to have overshooting responses for arbitrary initial conditions in state-space. Three finer notions of strong stability are introduced and necessary and sufficient conditions are established for each one of them. The invariance of strong stability under orthogonal transformations is also shown, and this enables the characterization of the property in terms of the invariants of the Schur form of the system's state matrix. The class of discrete-time systems for which strong and asymptotic stability coincide is characterized and links between the skewness of the eigen-frame and the violation of strong stability property are obtained. Connections between the notions of strong stability in the continuous and discrete-domains are derived. Finally, as application, the strong stability property is studied in the context of balanced realizations, general similarity transformations and state/output-feedback stabilization problems.

*** [J6] Vasilis Tsoulkas, Athanasios A Pantelous, Leonidas Dritsas and Christos I Papachristos, International Journal of Simulation Systems, Science & Technology “An Integrated e-Learning Solution for Control Systems Education and Future Perspectives”, Volume 12, Number 1, February 2011 http://ijssst.info/Vol-12/No-1/paper2.pdf Abstract- Technical characteristics of an innovative prototype e-learning platform using satellite communications for control theory courses are exposed. A detailed account of all necessary tools and mechanisms is presented enabling real time text, and audio/video based communication between tutors and learners. The provided end-user driven services include: a virtual classroom, offline operation, sharing of applications, private/public chatting, audio/video streaming. In addition a concise description of the pilot network architecture



depending on the DVB-RCS standard is presented justifying further the choice of the communications platform. Simulation results concerning the teaching of fundamental issues in Networked Control Theory within the proposed architecture are provided. Connections with hybrid configurations such as wireless terrestrial broadband technologies (DVB-RCS/ WiMAX, DVB-RCS/Wi-Fi) are further analyzed and justified. Finally some conclusive anticipated directions related to the future of modern control courses education in connection with state of art technological advances are explored.

[J7] George Bitsoris, Nikolaos Athanasopoulos and Leonidas Dritsas, “Stability, positive invariance and design of constrained regulators for networked control systems” Int. Journal of Control, Volume 85, Issue 10, 2012 , pages 1401-1413 (Version of record first published online: 09 May 2012 - see http://www.tandfonline.com/doi/abs/10.1080/00207179.2012.685763 )

Abstract: In this article the stability analysis and design of state-feedback regulators for Networked Control Systems (NCS) with bounded transmission delays, constant and unknown or time-varying, is investigated. First, the dynamics of the NCS is captured by ARMA models. Then, contrary to other approaches based on the choice of quadratic Lyapunov functions, polyhedral Lyapunov functions are chosen for both analysis and synthesis. Exploiting the fact that every matrix exponential can be decomposed to the weighted sum of its constituent matrices, conditions are leading to the determination of stability margins or stabilizing control laws are established by solving linear programming optimization problems. All results are derived in the actual NCS state space extending the applicability of the methods to the constrained control problem as well as the prespecified performance problem. Two examples illustrate the effectiveness of the approach.

*** “Recently Accepted for Publication” [J8] S. Theodoulis, V. Gassmann, P. Wernert, L. Dritsas, I.Kitsios, A.Tzes “Guidance and Control Design of a Class of Fin-Controlled Spin-Stabilized Projectiles” Submitted to: Journal of Guidance, Control, and Dynamics (AIIA) Date Submitted : 06-Oct-11 , Acceptance Letter received 11-May-2012 Abstract: This article presents a complete design of the guidance and autopilot modules for a class of fin controlled, spin-stabilized long range 155mm projectiles. The proposed concept is equipped with a nose-mounted course correction fuse containing all necessary electronic equipment and actuator devices. For trajectory control a skid-to-turn configuration with only two pairs of movable canards is used along with a co-axial motor for nose roll angle positioning. The main advantage of the overall configuration is that it maintains a high level of internal dynamic stability due to the highly spinning aft part whereas in the same time the forward part containing the guidance fuse remains easy to be fitted to any standard unguided projectile. The challenging task though is the design of the guidance and control modules which should counteract the very heavy coupling between the longitudinal/lateral projectile axes due to the aft part very high spin rate, the rapidly changing operating conditions and the limited actuator and sensor bandwidths. A systematic procedure in order to design both of these modules for the full system flight envelope is here described, whereas complete nonlinear simulations and Monte Carlo analysis results are provided thus proving the effectiveness of the considered concept.



Α.2 Two(2) Book Chapters

[B1] K. Alexis , G. Nikolakopoulos , A. Tzes and L. Dritsas “Coordination of Helicopter UAVs for Aerial Forest-Fire Surveillance”, pages 169 - 193 of the Book: “Applications of Intelligent Control to Engineering Systems” , International Series on Intelligent Systems, Control and Automation: Science and Engineering, 2009, Volume 39, Part II, 169-193, DOI: 10.1007/978-90-481-3018-4_7, by SpringerLink, Editor: Kimon P. Valavanis - Chapter available at http://www.springerlink.com/content/k37454wr84n57715/ - Book available at http://www.springerlink.com/content/978-90-481-3017-7/#section=60731&page=1

Abstract: In this article, a system using Unmanned Autonomous Quadrotor Helicopters (UqHs) for forest fire surveillance is presented. Quadrotor helicopters (equipped with inertial navigation systems, GPS, RF-transceivers and cameras) fly over the expanding perimeter of the fire and are used as the fire-front sensing systems. These helicopter-units patrol in a continuous manner and agree on varying rendez-vous with each other. These rendez-vous are set as waypoints in order to divide the surveyed fire-front length at equidistant portions. After the rendez-vous meetings between these helicopters, and the anticipated spread of the fire, new temporal-spatial rendez-vous points are predicted and transmitted to each UqH. These rendez-vous waypoints rely heavily on the fire-front spread algorithm (wind condition, moisture, fire fuel and the firefighters’ reaction. For more accurate observation, these UqHs fly at low-altitude and are prune to sudden wind-gusts. These wind-gusts can be detrimental not only to the flight performance of these units but also to their overall stability. In each helicopter, a back step propagation unit along with a stabilizing controller relying on the Constrained Finite Time Optimization Control (CFTOC) scheme is used. The CFTOC is responsible for attenuating the effects of the random wind-gust disturbances on tracking of the a priori reference trajectory. Simulation results are used to investigate the efficiency of the suggested concept.

***

[B2] G. Halikias, G. Leventakis, C. Kontoes, V. Tsoulkas and L. Dritsas “Design Issues of an Integrated Fire Detection System: Component and Sub-Systems Definition” - Published in the book: “Satellite Communications”, ISBN 978-953-307-338-5 by Intech Open Access publisher (Freely Available Online at http://www.intechopen.com/articles/show/title/design-issues-of-an-operational-fire-detection-system-integrated-with-observation-sensors Abstract: Novel design issues for the development of an early warning -state of the art- automatic fire detection/surveillance system are introduced. The basic building blocks and high-level architecture of the terrestrial components integrated with satellite data management and Earth Observation resources and sensors are defined and further analyzed in a consecutive fashion. Furthermore, distributed detection strategies of fire events given hardware and communication limitations are discussed and reviewed. In this context some connections with First Responders technical communication issues and other critical subsystems are provided. Finally, further research directions are suggested for the integration of existing technological platforms with future air and space based sub-systems within the proposed hybrid model setup. Keywords: Fire Detection System; Wireless



Sensor Networks; High Level System Architecture; Decentralized Detection; Earth Observation, DVB-RCS, TETRA interoperability.

Α.3 Twenty Seven (27) Reviewed Conference Papers (Proceedings)

[C1] L. Dritsas and S. Tzafestas “An algorithm for Robust Robot Control via the FCT and MRAC Techniques” Proceedings of the First European Conference on Informational technology for Organisational Systems (EURINFO ’88) Athens, Greece, May 1988.

*** [C2] S. Tzafestas, L. Dritsas, J. Kanellakopoulos “Robust Robot Control: A comparison of three techniques through simulation” 12th IMACS World Congress on Scientific Computation, Paris 1988.

*** [C3] S. Tzafestas, G. Stavrakakis and L. Dritsas “Performance Analysis of the Computed Torque Method for Robotic Manipulators with fast actuators” Proceedings of IEEE Intl Conference on Control and Applications (ICCON ’89), Jerusalem, April 3- 6, 1989 (Page(s):734-739) (http://ieeexplore.ieee.org/search/freesearchresult.jsp?history=yes&queryText=%28dritsas%29)

*** [C4a] A. Ikonomopoulos and L. Dritsas “Recent Advances in Robot Grinding” The European Robotics and Intelligent Systems Conference, Corfu, Greece, June 1991.

And also in

[C4b] Ikonomopoulos, A., Dritsas, L. (1992), "Recent advances in robot grinding", in Tzafestas, S.G. (Eds), Robotic Systems - Advanced Techniques and Applications, Kluwer, Dordrecht, pp.603-10.

*** [C5] George Nikolakopoulos, Anthony Tzes, Leonidas Dritsas, Yiannis Koveos “Multi--Parametric H-infinity Control of a Micro-Actuator” 16th IFAC World Congress Praha 2005

Abstract: In this article the control problem of a micro-actuator (μ-A) is considered. The μ-A is composed of a micro-capacitor, whose one plate is clamped while its other flexible plate's motion is constrained by hinges acting as a combination of springs and dashpots. The distance of the plates is varied by the applied voltage between them. The flexibility of the moving plate coupled to the dynamics of the plate's rigid-body motion results in an unstable, nonlinear system of distributed nature. Utilization of FEM can approximate the μ-A dynamics nonlinear-PDE to a finite nonlinear-ODE. The nonlinearity stems from the plate's rigid-body motion, while all flexibility effects are considered as additive linear-terms. A set point



controller composed of: a) a feedforward term for regulation at selected setpoints, and b) a constrained finite time optimal controller to handle any deviations from the equilibrium is synthesized. Simulation studies are used to investigate the efficacy of the suggested controller. Keywords: MEMs, Micro--Actuator, Optimal Control.

*** [C6] Anthony Tzes, George Nikolakopoulos, Leonidas Dritsas “Design and Sensitivity Analysis of Constrained Finite Time Optimal Controller for a Micro-Actuator” the 2005 Joint ISIC-13th Mediterranean Conference on Control and Automation (MED) Conference, June 27-29, 2005 Limassol, Cyprus (Proc. Page(s): 958- 963, Paper TuM06.2, DOI 10.1109/.2005.1467143 (IEEE Xplore)

Abstract: In this article a design and a sensitivity analysis is being performed towards the Constrained Finite Time Optimal Control (CFTOC) problem of a non-linear micro-actuator's model, whose one plate is clamped while its other plate's motion is constrained by hinges acting as a combination of springs and dashpots. The distance of the plates is varied by the applied voltage between them. The flexibility of the moving plate coupled to the dynamics of the plate's rigid body motion results in an unstable, nonlinear system of distributed nature. The controller is composed of: a) a feed-forward term for regulation at selected set-points, and b) a CFTO-controller to handle any deviations from the equilibrium. Multiple CFTO-controllers are being designed and applied to the non-linear system, and the sensitivity of the control action is tested towards the constraints, the prediction horizon, and the embedded uncertainty in the system, through extensive simulated test cases.

*** [C7] George Nikolakopoulos, Leonidas Dritsas, Anthony Tzes and John Lygeros “Adaptive Constrained Control of Uncertain ARMA–Systems based on Set Membership Identification” - Proceedings of the 14th Mediterranean Conference on Control and Automation” 2006, Ancona-June 28-30, Italy, 2006. DOI 10.1109/MED.2006.328814 (IEEE Xplore)

Abstract: In this article an adaptive Constrained Finite Time Optimal (CFTO) controller design is presented for unknown, discrete--time linear systems, whose dynamics are identified via Set—Membership Identification (SMI) algorithms. The controller consists of two modules: a) the Set Membership(SM)-Identifier that identifies the system's dynamics through the extended Recursive Least Squares (eRLS) while providing the vertices of an orthotope that contains the nominal identification parameter vector, and b) the CFTO-controller; the tuning of the controller is based on a batch tuning procedure. The controller's feasible operating region remains unchanged for: a) all SM-orthotopes that are subsets of the last orthotope for which the controller's tuning was based, and b) the calculated CFTO--controller remains constant for a large period of time. In the opposite case the control partition of the controller is recalculated (batch process) based on the current vertices of the identified SM--orthotope. Simulation results are presented that prove the efficacy and the validity of the suggested control scheme.

*** [C8] Leonidas Dritsas , Anthony Tzes, George Nikolakopoulos “Constrained Finite Time Control of Networked Systems with uncertain delay” - Proceedings of the 14th Mediterranean Conference on Control and Automation 2006, Ancona-June 28-30, Italy, 2006. DOI 10.1109/MED.2006.328765 (IEEE Xplore)



Abstract: In this article a Constrained Finite Time Optimal Controller (CFTOC) for Networked Controlled Systems (NCS) is presented for the case where: a) the induced network delays are uncertain and bounded, and b) there are constraints in the magnitude of the control action and the outputs/states of the system. Based on the assumption that the roundtrip latency time varies within known bounds, the uncertain network-induced delays are embedded in the system model resulting in a polytopic uncertain system. When the constraints on the input and the output/state are added, a CFTOC formulation of the control objectives yields an affine control law which guarantees both the stability and the performance of the closed loop, while satisfying the constraints. Simulation results are presented that prove the efficacy of the proposed control scheme.

*** [C9] L. Dritsas, G. Nikolakopoulos, and A. Tzes, “Constrained Optimal Control Over Networks with uncertain delays,” in Proceedings of the 45th IEEE Conference on Decision and Control, San Diego CA, USA, Dec. 13–15, 2006 Page(s):4993 – 4998 DOI 10.1109/CDC.2006.377636 (IEEE Xplore)

Abstract: In this article a Constrained Finite Time Optimal Controller (CFTOC) for Networked Controlled Systems (NCS) is presented for the case where: a) the induced network delays are uncertain and bounded, and b) there are constraints in the magnitude of the control action and the outputs/states of the system. Based on the assumption that the round–trip latency time varies within known bounds, the uncertain network–induced delays are embedded in the system model resulting in a polytopic uncertain system. A polytopic uncertain system model is developed for the cases where: a) the uncertain delay is smaller than the sampling period, and b) the delay is longer than one sampling period but can be decomposed into a fixed known part (integer multiple of the sampling period) and an uncertain part bounded by one sampling period. When the constraints on the input and the output/state are added, the control objectives can be cast in a CFTOC formulation, and the resulting affine control law guarantees both the robust stability and the robust performance of the closed loop system, while satisfying the constraints. Simulation results are presented that prove the efficacy of the proposed control scheme.

*** [C10] L. Dritsas, G. Nikolakopoulos, and A. Tzes, “Constrained Finite Time Optimal Control of a Micro – Capacitor” in Proceedings of the 32nd Annual Conference of the IEEE Industrial Electronics Society,( Page(s):3161 - 3165) IEEE- IECON'06, Paris – FRANCE, November 7 - 10, 2006 DOI 10.1109/IECON.2006.347557 (IEEE Xplore)

Abstract: In this article the control problem of a non–linear micro-capacitor (μ − C) is considered. Utilization of FEM can approximate the μ − A dynamics nonlinear-PDE to a finite nonlinear-ODE. The nonlinearity stems from the plate’s rigid body motion, while all flexibility effects are considered as additive linear-terms. The control methodology we employ is a combination of two ideas. First we use standard linearization techniques to compute PWA approximations of the original nonlinear system around multiple operating points. Next we employ the theory of Constrained Fine Time Optimal Controllers (CFTOC) in order to design (off–line) explicit switching controllers for the set of PWA systems obtained in the first step. The ensuing switched PWA controller is applied to the the original–nonlinear system. We investigate, via extensive simulations, the efficacy of using this control approach for output set–point tracking objectives.

***



[C11] L. Dritsas, G. Nikolakopoulos and A. Tzes “On the Modeling of Networked Controlled Systems” in Proceedings of the 15th Mediterranean Conference on Control and Automation, MED'07, June 27—29, Athens, GREECE DOI 10.1109/MED.2007.4433699 (IEEE Xplore) ( http://med.ee.nd.edu/MED15-2007/papers/T09-004-897.pdf ) Abstract: In this article modelling approaches for Networked Controlled Systems (NCS) with different types of varying communication latency times are presented. The embedded delays are unknown, bounded and depending on their size relative to the sampling period, four different models are offered. There is distinct treatment for delays longer than one sampling period, since these are decomposed to a term which is integer multiple of the sampling period and a residual which can be time-varying. The careful mixing of asynchronous (event–driven) and synchronized (sampled) signals can lead to discrete time uncertain and possibly switched systems, where classical control approaches could be applied.

*** [C12] Leonidas Dritsas and Anthony Tzes “Networked Controlled Systems: Modeling Issues for Robust Control” in Proceedings of the Workshop on Networked Distributed Systems for Intelligent Sensing and Control , Saturday, June 30, 2007 Kalamata, Greece , see (http://www.nd.edu/~pantsakl/kworkshop.htm) and the abstract at (http://med.ee.nd.edu/kalamata-2007/abstracts.pdf) Abstract: In this article1 modeling approaches for Networked Controlled Systems (NCS) with different types of uncertainly varying bounded transmission delays and static discrete–time control laws are presented. Different models are offered for each case, all linked to the objective of designing robust discrete-time controllers. It is analytically shown how the careful mixing of asynchronous (event–driven) and synchronized (clocked) signals can lead to discrete time uncertain (possibly switched) systems, where results from robust control analysis and synthesis can be applied. After showing the implications of these modeling results for control synthesis purposes, sufficient conditions for the robust stability are given for each approach and a comparison of the conservatism of results is discussed. The special case of constant and unknown delays is also handled.

*** [C13] Leonidas Dritsas and Anthony Tzes “Robust Output Feedback Control of Networked Systems” in Proceedings of the European Control Conference 2007 , Kos, Greece 2-5 July 2007 (http://ecc07.ntua.gr/ ) Abstract: This paper presents a design procedure for robust discrete–time feedback controllers for networked systems with uncertain input delays caused by the network’s attributes. Results concerning the robust stabilization of the closed loop Uncertain Time-Delayed System (UTDS) are presented for the case of static output feedback laws. relying on the Simulation results are presented that prove the efficacy of the proposed control scheme.

*** [C14] L. Dritsas, G. Nikolakopoulos and A. Tzes “Constrained Optimal Control for a Special class of Networked Systems” in Proceedings of the 2007 American Control Conference (ACC’07), New York City, USA , July 11-13, 2007 DOI 10.1109/ACC.2007.4283073 (IEEE Xplore)



Abstract: In this article a Constrained Finite Time Optimal Controller (CFTOC) for a special class of Networked Controlled Systems (NCS) is presented for the case where the uncertain induced network delays are bounded, unknown, fixed and restricted to be integer multiples of the sampling period. It is proven that the discretized version of the system under study is a switched/polytopic system whose placement on the vertices is governed by an uncontrolled network delay. When the constraints on the input and the states are added, the control objectives can be cast in a CFTOC–formulation, resulting in an affine switching control law. The presented simulation results prove the efficacy of the proposed control scheme.

*** [C15] Leonidas Dritsas and Anthony Tzes “Modelling Approaches and Robust Stability Conditions for Networked Controlled Systems with Uncertain Delays” in Proceedings of the 17th IFAC World Congress, July 6-11, 2008. Seoul Korea (p.6353--6358) - freely available at http://www.nt.ntnu.no/users/skoge/prost/proceedings/ifac2008/data/papers/1322.pdf Abstract: In this article two modeling approaches for Networked Controlled Systems (NCS) with different types of uncertainly varying bounded transmission delays and static discrete–time control laws are presented. Different models are offered for each case, all linked to the objective of designing robust discrete-time controllers. It is analytically shown how the careful mixing of asynchronous (event–driven) and synchronized (clocked) signals can lead to discrete time uncertain (possibly switched) systems, where results form robust control analysis and synthesis can be applied. After showing the implications of these modelling results for control synthesis purposes, sufficient conditions for the robust stability are given for each approach and a comparison of the conservatism of results is discussed. The special case of constant and unknown delays is also handled.

*** [C16] Leonidas Dritsas and Anthony Tzes “Constrained Control of Event-Driven Networked Systems” in the Proceedings of the 17th IFAC World Congress, July 6-11, 2008. Seoul Korea (p. 11600--11605) – freely available at http://www.nt.ntnu.no/users/skoge/prost/proceedings/ifac2008/data/papers/3609.pdf Abstract: This article focuses on the control of Networked Systems in which the packets are time-stamped and suffer from long (more than one sampling period) transmission delays. The inner sample arrival of the packet, coupled with other constraints posed by the system’s characteristics such as control and/or state saturation impedes the system’s performance. A constrained finite time optimal controller is designed for this system that is robust against the inner sample delays. The presented simulation studies investigate on the performance of the suggested controller.

*** [C17] Leonidas Dritsas and Anthony Tzes “Robust Stability Bounds for Networked Systems with Varying Delays”, The 17th Mediterranean Conference on Control & Automation, MED 2009, Thessaloniki, Greece, Jun 24 -26, 2009. (http://www.med09.org/ ) DOI: 10.1109/MED.2009.5164638 Abstract: This paper is concerned with Networked Controlled Systems (NCS) with uncertain, varying, bounded transmission delays and asynchronous discrete–time static control laws. It



is first shown that the delay variation gives rise to a discrete–time uncertain NCS model; robust stability analysis is carried out via a linear matrix inequality approach which, when combined with a directed parameter search, yields an estimate of robust stability bounds against any variations of the maximum allowable delay (constrained within one sampling period) that the closed–loop system can tolerate. The derived bounds are compared with other techniques relying on the singular values of the perturbed NCS–model. The presented simulation results prove the efficacy of the proposed control scheme.

***

[C18] Bitsoris Georges, Athanasopoulos Nikolaos, Dritsas Leonidas “Feedback Stabilization of Networked Control Systems” 2009 IEEE Multi-conference on Systems and Control July 8-10, 2009, Saint Petersburg, Russia (http://conf.physcon.ru/msc09/) DOI: 10.1109/CCA.2009.5280975

Abstract: In this paper the stability analysis and control synthesis problems for Networked Control Systems (NCS) with bounded transmission delays (constant and unknown or timevarying) are investigated. First, stability conditions for NCS described by ARMA models are established and a method for the determination of admissible delay range is developed. Then, a linear programming method for the design of linear state-feedback controllers guaranteeing the stability of the system for any delay belonging to a prespecified range is developed. Contrary to the usual approaches based on the use of quadratic Lyapunov functions, a polyhedral Lyapunov approach is adopted for both analysis and synthesis. A control synthesis numerical example is given to illustrate the reduction of conservatism of the tolerable delay range when compared to former results.

***

[C19] Leonidas Dritsas and Anthony Tzes “Robust Stability Analysis of Networked Systems with Varying Delays” European Control Conference 2009, Budapest, Hungary, August 23-26, 2009 (http://www.conferences.hu/ecc09/) Abstract: Robust stability conditions for Networked Controlled Systems (NCS) with uncertain, varying, bounded transmission delays and discrete-time static control laws are derived in this article. The delay uncertainty is shown to give rise to a discrete-time uncertain NCS model. The robust stability analysis is carried out via a linear matrix inequality approach which, when combined with a directed parameter search, yields an estimate of robust stability bounds on the maximum allowable delay (constrained within one sampling period) that the closed-loop system can tolerate. The presented simulation results show a drastic reduction of conservatism when compared with other techniques relying on the singular values of the perturbed NCSmodel.

*** [C20] L. Dritsas, V. Tsoulkas, A. Pantelous, and A. Tzes (2010) “Robust Performance Issues in Tracking Control over Networks”, Proceedings of ISMS 2010, 25 – 27 January, Liverpool, UK. (http://www.isms2010.org.uk/) page(s): 264 – 269. DOI: 10.1109/ISMS.2010.56 (IEEE Computer Society)



Abstract: This paper is concerned with the investigation of robust performance of linear tracking controllers affected by unmodelled delays acting in the loop. The incentive comes from the area of Networked Control System (NCS) where the inevitable network-induced (transmission) delays are either time varying or constant. The main contribution (based on extensive simulation work rather than strict mathematical proof) is that the tracking performance of (typical or more sophisticated) linear tracking control laws is drastically reduced when applied to NCS. The provided simulation results (i) demonstrate the impact of the network-induced delays on the tracking performance of single-input single-output NCS, (ii) provide initial guidelines for the tuning of the controllers and (iii) pave the road for further work to be done.

***

[C21] V. Tsoulkas, L. Dritsas, and A. Pantelous (2010), Technical Challenges in Network-Centric Control and Communication Systems, Proceedings of ISMS 2010, 25 – 27 January, Liverpool, UK ( http://www.isms2010.org.uk/) page(s): 256 – 263. DOI: 10.1109/ISMS.2010.55 (IEEE Computer Society) Abstract: This paper is concerned with the technical challenges arising from the emerging unification of network-centric control and communications. Specifically we are following two main directions. Firstly we briefly explore the current trends in the development of advanced satellite communications and hybrid satellite/terrestrial networks. Secondly we are concerned with the fast developing area of networked con-trolled systems (NCSs). In that respect relevant research problems are investigated in conjunction with possible future directions. Finally we conclude providing some specific research and development efforts related to state of the art integrated systems and services lying at the intersection of the above two categories and which are initiated and supported by international government and industrial organizations.

*** [C22] Leonidas Dritsas and Anthony Tzes “Robust Guaranteed–Cost Controllers for Networked Systems with Varying Delays” accepted at the 18th Mediterranean Conference on Control and Automation, held in Morocco, 23-25 June 2010 ( http://www.med10.org/ ) Abstract: This paper is concerned with the synthesis of robust guaranteed–cost controllers for networked systems operating under uncertain, bounded, time-varying transmission delays. The uncertainty of the transmission delay results in an uncertain discrete–time networked controlled system (NCS). The main contribution is a synthesis procedure for a static control law which not only robustly stabilizes the system against all admissible time–varying network–induced delays but also addresses performance issues expressed via a quadratic cost function. This delay–dependent procedure (a sufficient condition expressed via LMI) gives rise to a parameterization of the guaranteed–cost controllers allowing thus the investigation for an optimal controller which minimizes the upper bound of the closed-loop cost function. The provided simulation results demonstrate the efficiency of the proposed control scheme.

*** [C23] A. Pantelous, A. Karageorgos L. Dritsas and V. Tsoulkas “Higher Order Differential Delay Systems with Control Applications”, Proceedings of EUROSIM 2010, (7thEUROSIM Congress on Modelling and Simulation) September 6 - 10, 2010, Prague, Czech Republic ( http://www.eurosim2010.org )



Abstract: We are interested in solving and presenting some applications of higher order linear descriptor differential systems given by the expression:

with constant square coefficients and consistent initial conditions. Higher order linear descriptor systems can result from several types of linearization of general non-linear high order descriptor delay differential systems of the

general form: Typical applications where second order descriptor systems naturally arise involve multi-body systems and networked control systems (NCS). In our case, in order to solve such kind of systems, we apply the complex Weierstrass canonical form (WCF) and the Drazin inverse theory. Indeed, these two effective tools for the solution of descriptor systems have been systematically used in different areas of control and systems theory. Applying the WCF, two lower dimension sub-systems are obtained with a particular structure. A numerical example from the emerging area of NCS with constant and unknown network induced delays is presented as our basic motivation.

***

[C24] L. Dritsas, A. Zagorianos, A. Pantelous, V. Tsoulkas “Assessment of Linear Set–Point Controllers for a Direct Drive Nonlinear Pendulum” Proceedings of the UKSim – AMSS 13th International Conference on Modelling and Simulation (http://uksim.info/uksim2011/uksim2011.htm ) Cambridge University (Emmanuel College), 30 March – 1 April 2011 DOI: http://doi.ieeecomputersociety.org/10.1109/UKSIM.2011.46 Abstract: This paper is concerned with the design of linear set–point controllers for a specific nonlinear system: a motor driven pendulum. It is shown that when input constraints and delays are present, the synthesis procedure is non trivial. Even if the design is based on mature theoretical basis, extensive nonlinear simulations are the only practical way to ensure that the linear design offers acceptable tracking performance in a large operation range while respecting the requirements of input constraints and robustness.

***

[C25] V. Tsoulkas, A. Pantelous, L. Dritsas, C.Papachristos , “Hybrid Terrestrial-Satellite Architecture for Control Systems Education” Proceedings of the UKSim – AMSS 13th International Conference on Modelling and Simulation (http://uksim.info/uksim2011/uksim2011.htm ) Cambridge University (Emmanuel College), 30 March – 1 April 2011 http://doi.ieeecomputersociety.org/10.1109/UKSIM.2011.41

*** [C26] S. Theodoulis, I. Kitsios, L. Dritsas, A. Tzes and P. Wernert “Autopilot Strategies for Guided Gun-Launched Projectiles” (Proceedings of the 19th Mediterranean Conference on Control and Automation http://www.med2011.org/ Pages 248 - 253) - DOI: 10.1109/MED.2011.5983066 Abstract: The goal of this article is threefold: (1) Present a thorough model of a generic fin-guided ammunition involving the 6DoF nonlinear dynamics, equilibrium point computation,



Linear-Parameter Varying (LPV) modeling & stability analysis concepts (2) Investigate various structures of low complexity closed loop feedback controllers that could be potentially applied to fin-guided projectile autopilots. (3) Investigate several crucial modeling issues relevant to autopilot design such as state space transformations which avoid output feedback in favor of state feedback, actuator model incorporation, etc. Simulation results are presented which demonstrate the performance and complexity aspects of the proposed control schemes.

*** [C27] Nikolaos Athanasopoulos, George Bitsoris, and Leonidas Dritsas “A polyhedral approach to the stability analysis and feedback stabilization of networked control systems” (Proceedings of the 19th Mediterranean Conference on Control and Automation http://www.med2011.org/ Pages 1008 - 1013) - DOI: 10.1109/MED.2011.5983214 Abstract: In this note, the stability analysis and control design of Networked Control Systems (NCS) with bounded transmission delays, constant and unknown or time varying, is investigated using polyhedral Lyapunov functions. First, conditions guaranteeing stability are formulated for the equivalent augmented discrete-time system with structured uncertainties. Then, algebraic conditions leading to the computation of a linear state feedback controller for a NCS with bounded time varying delays are established. Both the stability analysis and synthesis problem are reduced to linear programming methods, a welcome consequence stemming from the choice of polyhedral Lyapunov functions. Two examples illustrate the effectiveness of the approach.

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